The present invention relates to a stator and a method of forming the stator.
A conventional stator for use in an electric motor and a method of forming the stator are disclosed by Japanese Unexamined Patent Application Publication (KOKAI) No. 2001-8417 wherein a plurality of core sheets having holes with concentric circles are stacked to form a stator core. Each core sheet has a plurality of recesses formed in the inner edge thereof thereby to form a plurality of slots in the inner circumferential surface of the stator core. The slots are in parallel with an axis of the stator core, in which a coil is inserted. Each core sheet also has a plurality of recesses formed in the outer edge thereof thereby to form a plurality of engaging grooves in the outer circumferential surface of the stator core. The engaging grooves are in parallel with the axis of the stator core, with which an engaging tool is engaged for skewing the slots. When the tool which is previously skewed is inserted into the engaging grooves and at the same time the grooves are inclined (or skewed) with respect to the axis of the stator core after the coil is inserted into the slots, each core sheet is rotated around the axis of the stator core thereby to skew the slots. Thus, the stator whose slots are skewed is formed.
However, since the outer circumferential surface of the stator core is a cylindrical surface, there has been a problem that it is troublesome to measure angle of inclination of the engaging grooves which are formed diagonally in the cylindrical surface. More specifically, since the width of the tool which is engaged with the grooves is smaller than those of the grooves, there exists play between the tool and the grooves in skewing the slots, so that the grooves may be waved. Since the slots have the coil inserted therein, skew angle of the slots is measured by putting a gauge in the grooves and measuring the angle of inclination of the grooves instead of measuring the skew angle directly. In this case, when the grooves are waved, the gauge is not put into the grooves. When the angle of inclination of the grooves is measured by image processing, the angle of inclination differs between points of measurement of each groove, so that it is troublesome to judge the skew angle.
In addition, the outer circumferential surface of the stator core is formed with fixation grooves for fixing the core sheets and alignment grooves for mounting the stator core on a housing of the electric motor as well as the engaging grooves with which the tool is engaged. When the slots are skewed, these grooves are also skewed. In this case, by so inclining the fixation grooves with respect to the axis of the stator core, when the core sheets are fixed by welding, torch needs to be diagonally moved, so that the cost of welding equipment is increased. Furthermore, by so inclining the alignment grooves with respect to the axis of the stator core, when the stator core is mounted on the housing of the electric motor by inserting pins into the alignment grooves to be aligned, it is troublesome to insert the pins into the alignment grooves, so that positioning accuracy deteriorates.
The present invention is directed to a stator of which fixed cost of a stator core and accuracy of skew angle of slots of the stator core are improved and a method of forming the stator.